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Nanoparticles do the work
Nanostructured metals join the list of materials that can reversibly change their dimensions enough to have potentially useful applications. Jörg Weissmüller and Herbert Gleiter at the Institute for Nanotechnology, Karlsruhe, Germany, and coworkers find that passing an electrical current through pressure-compacted platinum nanoparticles produces changes in the particles’ dimensions that are large enough to do mechanical work [Science, 300, 312 (2003)]. The reversible change, known as actuator strain, is about 0.1% for the nanoparticles. This is in the same range as the best results seen for commercial ferroelectric ceramics or carbon nanotube bundles, both of which are under study for uses like remote sensing, cantilevers that open or close engine valves, or artificial muscles in robots. The induced strain is proportional to the particles’ surface-to-volume ratio, and since porous metals with higher ratios are known, the researchers believe their initial results can be improved. But many factors yet to be explored will determine whether nanoporous metals can be competitive with other materials in actuator devices, they note
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